1. Field of the Invention
The present invention relates to a spouted bed device, a polyolefin production system equipped with a spouted bed device, and a process for producing polyolefins such as polyethylene and polypropylene using such a device and system.
2. Related Background Art
A spouted bed has the advantage that all the particles, even relatively large particles several millimeters in size which require an excessively high gas velocity for fluidization in a fluidized bed, circulate and are thoroughly mixed. Various studies have been conducted on spouted bed devices of differing construction which utilize a spouted bed. As used herein, “spouted bed” refers to a state characterized by the circulatory movement of particles wherein, under the action of a gas introduced at a high velocity from a gas inlet orifice provided at the bottom end of a cylindrical vessel, there forms a spout (sometimes referred to below as the “spout portion”) which has a dilute particle concentration near the center axis of the particle bed held within the vessel and in which particles flow upward together with the gas, and there also forms at the periphery of the spout an annular particle bed where particles fall in a moving bed state under the influence of gravity (see, for example, Terminology Dictionary of Powder Technology, 2nd Edition, edited by The Society of Powder Technology, Japan (The Nikkan Kogyo Shimbun, 2000), p. 321).
However, to make a spouted bed device commercially feasible, it is important that a stable spouted bed be fully sustained even with some fluctuation in the treatment conditions. For example, if a fluctuation in the velocity of the gas being introduced or the amount of particles held inside the device causes the spouted bed to become unstable, resulting in particles dropping down through the gas inlet orifice, operation of the device must be interrupted to recover the particles.